Yes, this definitely can lead to lower back pain. Some simple stretches you can do are to sit in a chair with good posture and just stretch your arms straight up over your head and lift at your ribs elongating the spine. You can also do the standing or laying down flat on the floor. Another great stretch is child's pose (look it online). If you can not do it on the floor you can sit on a chair at a table and put your arms on the table and slide back to get the same stretch. I do this a lot at work when my back gets stiff.

Also make sure to look up some hip and leg stretches. Tightness in your hips and hamstrings can cause lower back pain as well.

If the pain persists or gets worse, make sure to talk to your doctor. Back pain is the worst and left unchecked it can become a chronic problem. Hopefully as you do more and lose some weight and build some muscle you will have less pain.

also when you are walking, make sure that you are walking with good posture. I have found many times tucking the pelvis under so that you are all aligned helps tremendously with lower back pain